Many medical conditions in urology are rooted in a spastic dysfunction of the sacral reflex arcs. Examples of such conditions include pelvic pain (e.g., interstitial cystitis, endometriosis, prostatodynia, urethral instability syndromes), pelvic myofascial elements (e.g., levator sphincter, dysmenorrhea, anal fistula, hemorrhoid), urinary incontinence (e.g., unstable bladder, unstable sphincter), prostate (disorders (e.g., BPH, prostatitis, prostate cancer), recurrent infection (secondary to spastic sphincter, hypertrophied bladder neck) and neurogenic bladder dysfunction (e.g., Parkinson's Disease, spinal cord injury, stroke, multiple sclerosis, spasm reflex).
Urinary retention occurs when a patient cannot fully empty the bladder. Urinary retention may be either an acute or chronic condition. Causes of urinary retention can be a blockage to the flow of urine, or problems with nerves and muscles that regulate bladder function. Normally, the reflex to urinate is triggered when the bladder fills to 300-500 ml. The bladder is then emptied when the contraction of the bladder wall forces urine out through the urethra. The bladder, internal sphincters, and external sphincters may all be affected by disorders that create abnormalities in bladder function.
Urinary retention may be due to an overactive bladder which is characterized by uncontrolled, frequent expulsion of urine from the bladder. There may be reduced bladder capacity and incomplete emptying of urine. Spastic bladder may be caused by an inability of the detrusor muscle of the bladder to inhibit emptying contractions until a reasonable amount of urine has accumulated. Often, a strong urge to void is experienced when only a small amount of urine is in the bladder. Urinary retention may also be caused by difficulty in relaxing the urinary sphincter muscle. The sphincter may be spastic. Alternatively, the bladder neck may be hypertrophied. This difficulty in emptying the bladder may lead to urinary retention. In another type of dysfunction leading to urinary retention, both the detrusor muscle and the urinary sphincter(s) simultaneously contract resulting in urinary retention. A dysfunction associated with simultaneous contraction of both the detrusor and the urinary sphincter is called detrusor-external sphincter dyssynergia (DESD).
Other causes of urinary retention include interruptions in the nerve pathways to the bladder occurring above the sacrum. This nerve damage results in a loss of sensation and motor control and is often seen in stroke, Parkinson's disease, spina bifida, diabetes, pelvic surgery, or invertebral disc herniation, and most forms of spinal cord injuries. Sometimes no cause is found, and such idiopathic cases may be due to anxiety or aging.
Inability to control urination, also known as urinary incontinence, may be a result of urinary retention. This may be caused by abnormalities in bladder capacity or malfunction of control mechanisms such as the bladder neck and/or external urethral sphincter muscle that are important for the bladder's storage function. Either chronic or acute retention may lead to incontinence due to leakage of urine from an overfull bladder.
Irritating symptoms, such as urinary frequency and urgency, may be a result of urinary retention. Other irritating symptoms may include painful urination (dysuria), which may be a result of a urinary tract infection (UTI) caused by urine being held too long in the bladder. UTI with fever is a sign of potential severe kidney infection (pyelonephritis) and is a more worrisome situation as it may result in permanent damage of the kidney(s).
Stones may also form in the urinary tract of individuals with urinary retention caused by the stoppage of urine flow and/or infection.
Abnormal backup of urine from the bladder to the kidney(s), also known as vesicoureteral reflux (VUR), may develop as a means of releasing high pressure within the bladder. A UTI is of particular concern as VUR may place the patient at significant risk for a severe kidney infection by transporting infected bladder urine directly to the kidney(s).
In the past, physicians have tried a number of treatments for urinary retention. One treatment option is to use drugs to relax the bladder, such as anticholinergics such as propantheline and oxybutynin. However, these drugs do not act specifically towards the bladder and tend to reduce muscle tone throughout the body, an undesirable side effect. Intermittent catheterization is another treatment that can be used to empty the bladder; however, it often requires a skilled caregiver to place the catheter and is inconvenient to the patient. An indwelling catheter is another option; however, such catheters have several risks including infections and bladder stones. Another treatment option is to simply have the patient wear diapers or other protective type devices to prevent urine leakage and overflow from wetting clothing and/or bedding.
Another type of urological-neurological dysfunction relates to the prostate. The prostate is a partially glandular and partially fibromuscular of the male reproductive system. During aging, the prostate tends to enlarge (hypertrophy). This prostatic enlargement can lead to urethral obstruction and voiding dysfunction.
Prostatic enlargement is a common occurrence in older men. Lytton et al. (Lytton, B., Emery, J. M and Harvard, B. M. [1973] 99: 639-645) estimated that a 45 year old male had a 10% risk of prostate surgery by age 70. The U.S. Census Report estimates that there are 30 million people today over age 65. This segment of the population is projected to rise to 50 million over the next 30 years. Therefore, the number of men with prostatic enlargement also will increase. According to draft reports of the National Kidney and Urologic Disease Advisory Board, 425,000 prostatectomies were performed in the United States in 1989. Based on population growth estimates, the number of prostatectomies performed annually will rise to 800,000/year by the year 2020.
The urethra passes through the prostate (prostatic urethra) as it courses to the external urethral orifice. The prostate has five distinct lobes that are apparent at 12 weeks in the human fetus (Lowsley, O. S. Am. J. Anat. [1912] 13: 299-349.). Although the lobular branching found in the fetus is not visible in the prepubescent prostate, the lateral middle anterior and posterior lobes are used to describe the enlarged prostate.
A more recent viewpoint is that the prostate also is comprised of several morphologically distinct zones (McNeaL, J. Urol. Clin. North. Am. [1990] 17(3): 477-486). The majority of the glandular volume is composed of the peripheral zone (˜70-75%). The remainder of glandular volume is divided into the central zone (˜20-25%), the transition zone (˜5-10%) and the periurethral glandular zone (˜1%).
McNeal (1990) reported that BPH develops in the transition zone and the periurethral glandular zone. BPH nodules develop either within or immediately adjacent to the preprostatic sphincteric zone. The transition zone is a small region close to the urethra intimately related to the proximal urethral sphincter. The stroma of the transition zone is dense and compact, and is unusually susceptible to neurologically-induced disturbances of growth control. Its glands penetrate the sphincter, while sphincter muscle fibers penetrate the transition stroma. The periurethral glandular zone has a similar urogenic sinus origin as the transition zone.
BPH may be associated with increased amounts of stroma relative to epithelium (Bartsch, G., Muller, H. R., Oberholzer, M, Rohr, H., P., J. Urol. [1979] 122: 487-491). A significant portion of the stroma is smooth muscle (McNeal, 1990) which is under sympathetic nervous control. The contractile properties of this smooth muscle could account for the dynamic component of obstruction in BPH (Bruschini, H. et at. [1978] Invest. Urol. 15(4): 288-90; Lepor, H [1990] Urol. Clin. North Am. 17(3): 651-658).
In addition to sympathetic control of prostatic stroma, the prostate is highly innervated. The prostate nerve fibers enter the prostate from the posterior lateral aspect, with a concentration of ganglia near the junction between the prostate and the seminal vesicles (Maggi, C. A, ed. [1993] Nervous control of the Urogenital System, Harwood Academic Publishers; Higgins, J. R. A. and Gosling, J. A. [1989] Prostate Suppl. 2: 5-16).
Acetylcholine (ACH), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP) and noradrenaline fibers have been described in this gland. A rich plexus of ACH-positive nerve cell bodies is associated with secretory acini in all parts of the gland. Some of the ACH fibers also contain NPY neurons. VIP-containing neurons have been found associated with ACH-containing nerve cell bodies. Occasional neurons have been found between the ACH-staining nerve fibers, suggesting that both NPY and noradrenergic neurons supply smooth muscle (Higgins, J. R. A and Gosling, J. A [1989] Prostate Suppl. 2: 5-16).
Autonomic nerves are distributed evenly between the central and peripheral zones of the prostate (Higgins, J. R. A. and Gosling, J. A [1989] Prostate Suppl. 2: 5-16). Peripheral neuronal control is similar. In addition, there is no difference in the type of nerve fibers, found associated with either epithelial or stromal elements of the gland.
The anatomical studies of nerve fiber types in the prostate, coupled with other studies of innervation of prostatic stroma (Brushing H, Schmidt, R. A, Tanagho, E. A, [1978] Invest. Urol. 15(4): 288-290; Watanabe, H., Shima, M., Kojima, M., Ohe, H. L. [1989] Pharmacol. Res. 21 (Suppl. 2): 85-94) suggest that cholinergic innervation influences epithelial behavior, while adrenergic innervation influences stromal tonus (excitability). These observations have provided a rationale for the use of, for example, alpha blockers in the treatment of BPH. The effects of alpha blockers (Downie, J. W. and Bialik, G. J. [1988] J. Pharmacal. Exp. Ther. 246(1): 352-358) can also account for improvements in symptoms of BPH as a result of dampening of dysfunctional striated sphincter behavior by the alpha blockers.
Studies have also shown that there are several tachykinins (for example, substance P [SP], calcitonin gene related peptide [CGRP], neurokinin A, bradykinin, and nerve growth factor [NGF]) that can influence the tonus of smooth muscle (Hakanson, et al., [1987] Neuroscience 21(3): 943-950). Neurotransmitter receptors have been quantified throughout the prostate (e.g., NPY, VIP, SP, leu-enkephalin (L-enk), met-enkephalin, 5-HT, somatostatin, acetylcholinesterase positive fibers (ACTH), and dopamine beta-hydroxylase (DBH) (Crowe, R., Chapple, C. R., Bumstock, G. The Human Prostate Gland: A Histochemical and Immunohistochemical Study of Neuropeptides, Serotonins, Dopamine beta-Hydroxylase and Acetylcholinesterase in Autonomic Nerves and Ganglia). There is some variation in receptor density at different prostatic sites in benign prostatic hyperplasia.
Changes in electrophysiologically recorded cellular behavior and in concentration of neuropeptides within the spinal cord have been shown to be a secondary consequence of mechanical pinch to the tail muscles of a rat, catheter stimulation of the posterior urethra, and electrostimulation of a peripheral nerve. Dyssynergia between the detrusor and the urethral sphincter is a significant finding in prostatodynia patients. Denervation of the prostate has been shown to produce dramatic changes within the prostatic epithelium. Thus there is evidence that experimentally induced alterations in neurological influences can be produced in the sacral, spinal cord, bladder or urethra through mechano-, electron, chemical or thermal (microwave, laser) methods to change irritative behavior. However, there have been no known attempts to use neurotoxins for therapeutic applications.
There is poor correlation between the degree of prostatic enlargement and the severity of symptoms. While 80% of men age 70 show BPH on transrectal ultrasound scans, only 20% seek surgery (Coffey, D. S. and Walsh, P. C. [1990] Urol. Clin. North Am. 17(3): 461-475), the treatment of choice for BPH (Fowler, F. J. Jr., Wennberg. J. E., Timothy, R. P. [1988] J. Amer. Med. Assoc. 259(20): 3022-3028). Symptoms of irritation may far exceed symptoms expected based on the size of the prostate. Symptoms may improve after surgical treatment of BPH by procedures such as transurethral resection of the prostate (TURF) (Christensen, Aagaard, M. M. J., Madsen, P.O. [1990] Urol. Clin. North Am. 17(3): 621-629), balloon dilation (Dowd, J. B. and Smith, J. J. III [1990] Urol. Clin. North Am. 17(3): 671-677), or prostatic hyperthermia (Baert, L., Ameye, F., Willemen, P., et al. [1990] J. Urol. 144: 1383-1386). However, symptoms persist in as many as 15% of all BPH patients (Baert, L., Ameye. F., Willemen, P., et al. [1990] J. Urol. 144: 1383-1386; Wennberg, J. E., Mully, A. G., Hanley, D., Timothy, R. P., Fowler, F. J., Roos, R. P., Barry, M. J. et al. [1988] J. Amer. Med. Assoc. 259: 3027-3030). Up to 25% of BPH patients have secondary procedures in long term follow-up studies, suggesting that surgical approaches do not address the fundamental mechanisms that produce BPH, i.e., the faulty neurological influence (control mechanism) on the integrity of the lower urinary tract.
The need for repeated surgeries, the morbidity and mortality associated with TURP and the cost of surgery have led to the development of some non-surgical approaches such as androgen ablation (McConnell. J. D., [1990] Urol. Clin. North Am. 11(3): 661-670) and the use of alpha blockers discussed above, but few medical or surgical treatments to date have produced a restoration of void behavior to normal state (flow rate of about 25 cc/sec and void volume of about 400 cc).